Dimethyl structure

Furan, 2,5-diacetoxy-2,5-dihydro-dipole moments, 4, 556 Furan, 3,4-diacetyl-2,5-dimethyl-structure, 4, 539... 

Hetero[13]annulene, bis-dehydro-dimethylated structure, 7, 716 H etero[ 17]annulenes H NMR, 7, 719, 721 restricted structure, 7, 720 Heteroaromatic compounds reactions... 

Imidazole-5-thione, 4,4-diphenyl-tautomerism, 5, 368 3 H-Imidazole-2-thione, 1,3-dimethyl-structure, 5, 367 Imidazole-2-thiones acidity, 5, 367 betaines, 5, 372 synthesis, 5, 481 tautomerism, 5, 367 3H-Imidazole-2-thiones synthesis, 5, 473, 6, 992 Imidazolides deacylation, 5, 453 mass spectra, 5, 360 phosphoric acid reactions, 5, 454 reactions, 5, 451-453 Imidazolidine, l-alkyl-3-phenyl-N-oxidation, 5, 427 Imidazolidine, 1,3-benzyl-2-phenyl-oxidation, S, 427... 

Methylbutene-l, 4-methylpentene-1 and 5-methylhexene-l represent a homologous series. Thus, it is conceivable that intramolecular hydride shift polymerization will also occur with the latter two monomers. Indeed NMR spectra seem to suggest that a predominantly 1,4 and 1,5 type isomerization polymerization occurs when 4-methylpentene-1 and 5-methylhexene-l are reacted with catalysts of the Lewis acid type at low temperatures (—73° C.) (163). According to the NMR evidence, low temperature cationic poly(4-methylpentene-l) shows only 2 sharp peaks, characteristic for the CH3 and CH2 groups. This is in agreement with a gem. dimethyl structure of the a,a-dimethylbutane type ... 

In case of poly(isobutylene-co-P-pinene) the characteristic resonances associated with the gem-dimethyl structures in Ae 6 = 0.8 to 1.1 range provide an ideal diagiK -tic tool for the analysis of dyad distributions. The relative proportion of resonances determined at 6 = 0.8,1.0 and 1.1 reflect the relative proportion of uncrowded, half-crowded and fuUy-crowded gem-dimethyl groups respectively. Thus... 

In a model synthesis <81CC524>, a nitro-Michael addition of the readily available nitroalkyl pyrrole 36 to mesityl oxide was used to introduce a geminally dimethylated structural element into an AD component rac-39 for the desired chlorin. Reduction of the nitro function in rac-37 leads to the desired AD dimer rac-38 which is combined in the presence hydrobromic acid with the well known a-bromo-a -bromomethyl dipyrromethene 40 after acid induced ester clevage and decarboxylation to yield the tetrapyrrolic biline rac-41. In the final step the linear tetrapyrrole rac-41 undergoes oxidation and cyclization in the presence of copper(II) acetate to give the copper chlorin. The cyclization occurs via the enamine tautomer of rac-41 by nucleophilic attack of the enamine structure on the bromo imine part of the linear tetrapyrrole. 

Incorporation of chiral centers into cyclic structures produces some interesting consequences. If we consider dimethylcycloalkanes, the cis-dimethyl structures will be achiral, since they possess a plane of symmetry. A /rans-dimethylcycloalkane will be chiral when the ring is odd. When the ring is even, whether it will be chiral or achiral will depend on the substitution pattern. Inspection of the dimethylcyclo-propanes and dimethylcyclobutanes serves to illustrate these stereochemical features. The three possible stereoisomers of 1,2-dimethylcyclopropane are ... 

Incorporation of chiral centers into cyclic structures produces some interesting consequences. If we consider dimethylcycloalkanes, the ds-dimethyl structures will be achiral, since they possess a plane of symmetry. A rran5-dimethylcycloalkane... 

Solution 11 All the hydrogen atoms are eclipsed in the planar conformation of cyclobutane. The folded ring system has skewed hydrogen interactions. There are six possible isomers of dimethyl-cyclobutane. Since the ring is not held in one particular folded conformation, deviations of the ring planarity need not be considered in determining the number of possible dimethyl structures. 

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